A human resources problem that I am experiencing is a shortage of human resources of community members who are willing, available, and have the skills to work on a variety of useful initiatives. Is anyone on this list aware of research that talks about motivations of long-term contributors? In particular, I'd be interested in research that suggests ways to convert productive, relatively new editors (say, 50-500 edits) into long-term community members who are likely to develop into long-term, productive Wikimedians.